4306e07775
Includes refactoring to share code with (Source)ExtensionBuilder. Change-Id: If3cc66fa9f868d23ef756f80bc2f447cb534c5d1 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/268763 Commit-Queue: Johnni Winther <johnniwinther@google.com> Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>